I. Field of the Invention
This disclosure relates to a method and apparatus for automatically forming battery straps and intercell connections in a storage battery.
II. Description of the Prior Art
Various techniques exist for forming battery straps and making intercell connections in a battery. See U.S. Pat. Nos. 3,703,589; 3,652,337; 3,579,386; 3,519,489; and 3,514,342.
In Patent No. 3,703,589, alternate plates in each compartment of a battery are electrically interconnected by a crossbar. Conductive bar-like members extend upwardly from the crossbars on opposite sides of the compartment partition wall and they are electrically interconnected at their upper ends by conductive pins which extend through an aperture in the partition wall. The conductive bar-like members are cast in molds formed in the battery but the crossbars are not. During the casting process the conductive bar-like members are connected to the conductive pins. However, a further step is required to seal the connection to the partition wall by applying pressure through the bar-like members to opposite ends of the pins.
A cast on method of forming straps to battery plates is described in U.S. Pat. No. 3,652,337. A number of alternatively spaced positive and negative plates with separators therebetween form a cell group which ultimately forms one cell of the finished battery. The lugs of the plates within the cell group form two rows of lugs, a positive row and a negative row. These lugs are cleaned, coated with a lead alloy melt and then rapidly transferred to a plate strap casting station where the lugs are immersed into a mold filled with molten-strap-forming material.
U.S. Pat. Nos. 3,818,985; 3,815,623; 3,565,162; 2,199,598; and 1,336,767 all disclose methods for handling or casting molten metal. Certain of these patents disclose methods for continuous or simultaneous pouring for casting several parts. U.S. Pat. Nos. 3,921,704; 3,371,186, and 2,364,615 disclose means of casting molten metal and minimizing the oxidation thereof during the casting process.
More recently a method of molding connectors in electrical accumulators has been disclosed in U.S. Pat. No. 3,988,169. The assembly method according to that patent "permits placement of the plates into their respective cells prior to their interconnection, and subsequently allows simultaneous interconnection of plates and forming of intercell connectors between adjacent cells which are separated by a partition wall, by flowing molten lead or lead alloy through an aperture in the partition wall between the cells". The method requires the forming of a "channel adjacent the plates of like polarity in each group of plates".
While U.S. Pat. No. 3,988,169 overcomes some of the disadvantages of prior art techniques, this patent discloses a method which is dependent upon the hand manipulation of battery plates and molds within the battery case, with attendant quality control and misalignment problems. Similarly, since polypropylene, a standard battery case material, melts below the temperature of molten lead, the method by which that lead is introduced adjacent and through the plastic aperture is of particular concern. See U.S. Pat. No. 3,874,933 which relates to the casting of lead through a plastic aperture. U.S. Pat. No. 3,988,169 does not describe means for introducing molten lead into the channels described therein nor are the problems relating to the bonding which is obtained between the molten lead and the battery lugs and/or between the lead in adjacent compartments considered by this patent. See U.S. Pat. Nos. 3,652,337; 3,238,579; 3,229,339; 3,087,005; 2,799,905; and 2,454,053 for discussion of various approaches taken to overcome problems encountered when trying to cast straps to the lugs whith a "cast on" method. Temperature gradients within sections which are successively cast would be expected to result in differential hardening and the formation of oxide barriers between different portions of the intercell connection and/or strap. These oxides or dross will substantially increase the internal resistance of the battery or cell, and may encourage corrosion which could, under certain conditions cause premature failure or sparking, the latter of which may have explosive consequences. Use of standard ladling techniques to cast the straps and intercell connections of the battery of U.S. Pat. No. 3,988,169 also present certain fill control and premature hardening problems since the disclosed molding channel is relatively deep and a steady hand would be required to pour a thin, accurate stream of molten lead into the channel without splashing lead against the upper portions of the side walls of the mold.